I. Field of the Invention
The present invention relates generally to fluid control valves and, more particularly, to a directional control valve for controlling fluid pressure to and from a fluid actuated device.
II. Description of the Prior Art
Fluid powered devices, such as fluid powered lifts and jacks, are widely employed in industry. Such devices are typically pneumatically or hydraulically powered and include an expansible chamber or fluid powered motor for converting pressurized fluid flow to mechanical movement. Thus, by connecting the fluid device to a source of fluid pressure, the fluid device produces mechanical movement in one direction while, conversely, exhaustion of the fluid pressure from the fluid powered device produces mechanical movement in the opposite direction.
In order to supply the desired amount of pressurized fluid to or from the flid powered device, a bidirectional control valve is typically connected with the fluid powered device. These control valves are selectively operable to connect the fluid powered device with a source of fluid pressure, or alternatively, to exhaust pressurized fluid from the fluid powered device. Such previously-known control valves are conventionally actuated by solenoids, a hand lever, pushbuttons, a foot pedal, and the like. In all these cases, however, the valve body is stationary and actuation of the valve means is effected by a spool or similar valve member moving within the valve body and operable to effect directional fluid flow through the valve body.
These directional control valves are disadvantageous in that the valve member must be manually moved to its neutral or inoperative position after the desired degree of actuation of the fluid device is obtained. Failure to immediately do so, of course, requires the reverse operation of the directional control valve in order to return the fluid device to the desired position.
A further disadvantage with many of these previously-known directional control valves, and particularly the solenoid actuated valves, is that while the direction of fluid flow through the control valve is controllable, the flow rate through the control valve is not. Consequently, with this type of previously-known directional control valve, accurate positioning of the fluid powered device is difficult, if not altogether impossible. Moreover, when accurate positioning of the fluid powered device is required, the control valve is actuated in a reiterative fashion until the desired position of the fluid device is obtained. Such a reiterative process is time consuming in practice and therefore costly.
A still further disadvantage of these previously-known directional control valves is that the valve body is stationary relative to the fluid device movable member so that the valve body is stationary regardless of the degree of actuation of the fluid device. This arrangement, however, is disadvantageous in that it prohibits the operator from controlling the movement of the fluid powered device by touch or feel when positioning the fluid powered device.